Interactions between phytase and different dietary minerals in in vitro systems

An in vitro experiment was conducted to evaluate the effect of different dietary minerals on phytate hydrolysis by microbial phytase enzyme and to measure the residual phytate content after phytate digestion. Calcium (0, 6, 8, 10 g kg of diet), Fe (0, 70, 80, 90 mg kg of diet), Zn (0, 30, 40, 50 mg kg of diet) or Na (0, 1.5, 2.5 and 3.5 g kg of diet) were incubated with a Na-phytate solution, with phytase enzyme (500 FTU kg of diet) at pH 2.5 or 6.5. The phytate concentration was set at 0.27% to mimic the phytate level in a typical corn-soybean meal-based poultry diet. Inclusion of Ca, Zn and Fe significantly (p < 0.05) reduced the phytate phosphorus hydrolysis at both pH values but the effect was strongest at pH 6.5. Irrespective of the pH, adding Na also inhibited (p < 0.05) phytate phosphorus hydrolysis; however, the negative effect was more pronounced at pH 2.5 than 6.5. Residual phytate content (mg) after phytate digestion was higher (p < 0.05) at pH 6.5 than at 2.5 in the presence of Ca, Zn and Fe. The reverse was the case in the presence of Na. These in vitro results demonstrated that increased concentrations of dietary Ca, Fe, Zn and Na could reduce phytate phosphorus hydrolysis, but such a response would need to be tested in animal feeding trials.